1. Field of the Invention
The present invention relates to a control apparatus for an on-vehicle electricity storage device such as a 12-volt lead storage battery.
2. Description of the Related Art
Conventional electrical power generation control apparatuses for vehicles are known, which perform control operations in such a manner that the inter-terminal voltage of an on-vehicle battery such as a 12-volt lead storage battery, which is provided for operating various on-vehicle electrical devices, is measured, the amount of energy discharged from the battery is calculated based on accumulated products each of which is obtained by multiplying the amount of decrease in the inter-terminal voltage by the time during which the inter-terminal voltage has decreased, and when the amount of energy discharged from the battery exceeds a predetermined value, a generator, which is driven by an internal combustion engine for charging the on-vehicle battery, is controlled so as to stop the power generation or so as to decrease the amount of power generation (see, for example, Japanese Unexamined Patent Application, First Publication No. Hei 07-212986).
In such an electrical power generation control apparatus for a vehicle, because the amount of energy discharged from the battery is calculated based on accumulated products each of which is obtained by multiplying the amount of decrease in the inter-terminal voltage by the time during which the inter-terminal voltage has decreased, it is determined that the battery has discharged (i.e., the state of charge of the battery has decreased) when the inter-terminal voltage of the on-vehicle battery has decreased.
In general, when the amount of energy being discharged from the battery is decreased, i.e., the amount of energy being taken out from the on-vehicle battery is decreased, the power generation by the generator is stopped, and the charging operation for the battery is also stopped; however, in the case of a 12-volt lead storage battery or the like, the inter-terminal voltage may remain steady the charging is stopped, but may begin to decrease after the lapse of a certain time after the charging is stopped.
In such a case, there is a time lag between the timewise change in the inter-terminal voltage of the on-vehicle battery and the timewise change in the state of charge of the battery; therefore, a problem is encountered in that the timewise change in the state of charge cannot be accurately estimated. When the timewise change in the state of charge of the on-vehicle battery cannot be accurately estimated, it is difficult to appropriately control the power generation operation of the generator which is provided for charging the on-vehicle battery, which may lead to a reduction in the useful life of the on-vehicle battery because the on-vehicle battery is frequently placed in an over-discharged state, and also which may lead to a degradation of the fuel economy of the vehicle because the generator is frequently operated by the internal combustion engine.